Patient gas delivery apparatus of the kind having a mask worn by a patient and a gas delivery conduit attached to the mask are commonly used in the analysis and treatment of respiratory disorders. The gas conduit delivers a gas under pressure to the patient. It is necessary that the gas conduit is detachable from the mask to facilitate cleaning.
Patient gas delivery apparatus typically includes at a minimum, a gas delivery conduit and a nose or full face mask. In some cases it is a clinical requirement that additional components be included, such as means for CO2 washout, for example, vents, anti-asphyxia valves and the like. In some cases, these additional components must be assembled in between the gas delivery conduit and the mask. Problems with prior art assemblies include:
(a) They may be inadvertently assembled without the additional components
(b) They may be incorrectly assembled, for example, incorrectly aligned
(c) During the course of treatment, the patient may inadvertently remove or dismantle the assembly and incorrectly reassemble it.
Further, known mask cushions are usually molded from a relatively soft, resilient, elastic material and they are shaped during manufacture to match the facial contours of an average intended wearer. However, a problem with the known types of masks is that, because individuals vary so much from the average, the masks must be forced against their inherent resiliency to deform and so adapt to the shapes of the users in order to avoid gas leakage. This requires that the masks be secured firmly by retaining straps or harnesses in order to prevent air leakage.
Flow generators are typically utilized to deliver a breathable gas (i.e., air) to a patient wearing the mask. In CPAP treatment, gas is delivered to the patient's airways at about 2–30 cm H2O above atmospheric pressure. The flow generator is generally connected to flexible tubing which is secured to the mask worn by the patient. If the flow generator's operation is interrupted as a result of a power outage or other mechanical or electrical failure, there may be a significant build up of carbon dioxide in the mask as the patient's exhaled air is not washed out of outlet vents which are usually contained in the mask. This may present a health problem to the patient.
There have been numerous patents which have addressed some sort of safety valve for gas or air delivery masks. An example of such a patent is U.S. Pat. No. 5,438,981. This patent discloses a counter balanced, rigid valve element which depending on the gas flow, either covers an opening to the ambient air or covers the gas flow airway such that the air or breathing gas is forced out into the ambient air opening. However, this system suffers from being a fairly complicated and expensive system whose correct operation relies on a counter balanced moving part moving relative to its housing. Further, if any condensation from the air gets on or around the balanced valve element, the operation of this valve element can be compromised. This valve is also difficult to clean.
Applicant's international PCT patent application No. PCT/AU97/00849 discloses a valve having a single valve element. However, whilst being simpler than preceding valves of this type, the valve shown in PCT/AU97/00849 still relies on the use of a rigid valve element moving relative to its housing and biased by magnets.